NAT I have a BEFSR41 wired Linksys cable/DSL router w/ 4 port switch and i cant figure out how to open the NAT.

First, you need to get into the user interface for the router.  To do that, just open your web browser, type in 198.168.1.1 & hit enter.  A login prompt will pop up if you're able to access the router.

If you've never done this before, the username is blank & the password is admin

What, exactly do you want to do with the NAT firewall?

To enable/disable NAT: click on setup, then click on advanced routing.

To filter Internet NAT redirection: click on security, then click on filters.

You can find this information in the User guide provided by LinkSys at:

http://www.linksys.com/servlet/Satellite?c=L_CASupport_C2&childpagename=US%2FLayout&pagename=Linksys%2FCommon%2FVisitorWrapper&cid=1166859876500&displaypage=download

Select your version number, then click on User Guide when it comes up.  User guides & Interfaces for the BEFSR41 are almost identical on every version.